The present invention relates to therapeutic devices and, more particularly, to therapeutic devices for exercising immobilized limbs in order to reverse the effects of osteoporosis.
When human limbs are immobilized for prolonged periods of time, whether due to paralysis or to encasement in a cast, a condition known as osteoporosis can occur. Osteoporosis is a deossification with absolute decrease in bone tissue resulting in, among other things, structural weakness of the bone. Many therapies have been developed to slow down or reverse osteoporosis. For example, since it is well-known that human bones are sensitive to electric current, attempts have been made to utilize electric current to promote osteogenesis, or formation of bone.
Although osteogenesis can be stimulated by delivering electric current to bones by means of internal electrodes, there are disadvantages to this type of treatment. One disadvantage is that stimulation of bones by electric current has only a slight effect on increasing bone formation.
More recently, it has been found that the vibration of bones can reverse osteoporosis. This relationship has been found in bones which have been made osteoporatic by previous plaster cast immobilization, such as that used to treat a fracture of the leg bone. It is believed that the application of mechanical vibration to the limbs deforms the bones within the limbs and generates an endogenous electric current due to the piezo-electric effect of the bone matrix. Osteoporatic bones in the legs have been treated by the application of mechanical vibrations to the soles of the feet. A disadvantage with this type of treatment is that the transmission of vibrations through the bones of the legs tends to vibrate and hence build up the bones in a single plane or along one axis, to the exclusion of other bones or along other axes.
In a specific example, vibration applied to the lower leg vibrated the knee at a single angle and missed stressing many critical bone surfaces along the leg. Of course, the application of vibrations to the leg or other limb at a plurality of locations may counteract this disdvantage to some extent, but this would greatly lengthen the time and expense of the treatment.
Another problem encountered with this type of therapeutic treatment is that it is difficult to determine the magnitude of the vibrations actually felt by the bones of the legs receiving the vibrations. For example, if the mechanical vibration is applied to the bottom of the foot, the soft tissue in that area and in the knee absorb some of the vibration, so that it is not possible to determine the amplitude of vibration actually felt by the bone simply by measuring the amplitude of the vibration applied to the limb. This relationship between the applied vibration and the vibration actually felt by the bones renders conventional vibrators unacceptable for use in giving reproducible results in terms of knee and leg treatment.
Accordingly, there is a need for a therapeutic device which applies external mechanical vibrations to the limbs of a subject and thereby vibrates the bones of those limbs sufficiently to reverse the effects of osteoporosis. Furthermore, such a device should be designed to vibrate the bones of the subject's limbs in a number of planes so that all of the bone surfaces are vibrated sufficiently to reverse the effects of osteoporosis. In addition, the device should include means for detecting the resultant vibration of the bones of the subject's limbs so that the magnitude of the vibrations actually felt by the bones can be controlled.